1. Field of the Invention
This invention relates to a reproducing method of reproducing a disc to be reproduced at a constant angular velocity method and a reproducing apparatus for reproducing the disc.
2. Description of the Prior Art
A reproducing method of the modified constant angular velocity (MCAV) is known. This prior art modified constant angular velocity method is as follows:
Data are recorded on a disc at a predetermined data linear density in the circumferential direction of the disc irrespective of a radial position of a track where the data are stored. Since this disc is reproduced at a constant angular velocity (CAV) by rotating the disc at a constant rotational speed, a data rate of the reproduced data changes with the radial position of the reproducing head. Therefore, there is a problem that it is difficult to process the reproduced data with a single processing circuit, such as a waveform equalizing circuit, or a clock reproducing circuit, having a single time constant or single processing speed.
In the modified constant angular velocity method, the data rate varies with the radial position of reproduced data, which is inconvenient for some applications. Another prior art reproducing method of a modification of the modified constant angular velocity method is disclosed in Japanese patent application provisional publication No. 63-161564. This prior art reproducing method reproduces a disc with two heads which respectively access an outer track and an inner track at the same time such that a total data rates of these heads are constant by controlling radial position of the heads and the reproducing circuits.
However, in the above-mentioned reproducing apparatus employing the modified constant angular velocity method, the data rate of the reproduced data for processing circuits thereof also varies with the radial position of the data recorded, so that reproducing circuits must process data signals having data rates varying over a relatively large range. Therefore, waveform equalizing circuits thereof and clock reproducing circuits for bit synchronization, which generally comprises a PLL circuit, require setting of optimum time constants for these circuits. That is, in such a prior art disc reproducing apparatus, the reproducing circuits or the clock reproducing circuits require high performance parts or the trimming of circuit constants to realize these circuits. Moreover, the scale of the reproducing circuit becomes larger.